Bombus (Alpinobombus) polaris Curtis, 1835

Risch, Stephan, Roberts, Stuart P. M., Smit, Jan, Wood, Thomas J., Michez, Denis & Reverté, Sara, 2023, The new annotated checklist of the wild bees of Europe (Hymenoptera: Anthophila), Zootaxa 5327 (1), pp. 1-147 : 31-32

Bombus (Alpinobombus) polaris Curtis, 1835 and Bombus (Alpinobombus) pyrrhopygus Friese, 1902

There is an ongoing debate as to whether the Nearctic taxon polaris Curtis, 1835 and Palaearctic taxon pyrrhopygus Friese, 1902 should be considered as conspecific or heterospecific.

Based on a lack of statistical differentiation in CLGS, Martinet et al. (2018b) consider these taxa as conspecific, grouping them under the oldest available name Bombus (Alpinobombus) polaris Curtis, 1835 . These authors also base their argument on the fact that a previous study by Williams et al. (2015) showed no differentiation in the slowly-evolving PEPCK nuclear gene between these two taxa (despite showing a significant differenciation based on COI).

However, a detailed revision of the world Alpinobombus Skorikov, 1914 species by Williams et al. (2019) concluded that Bombus polaris Curtis, 1835 and Bombus pyrrhopygus Friese, 1902 could be considered as two differentiated species. The decision of Williams et al. (2019) is based on the following evidence: (i) a species coalescent in the COI marker demonstrated by the Poisson-tree-process procedure (cf. Zhang et al. 2013); (ii) diagnostic differences in the 16S gene; (iii) differences in morphology and colour patters between both taxa. Furthermore, according to Williams et al. (2019), the lack of statistical differentiation in CLGS cannot be used as a convincing argument of conspecificity, as the absence of co-occurrence between both taxa might have removed any selective pressure that might otherwise have enhanced barriers to interbreeding by driving evolutionary divergence in sex pheromones. Williams et al. (2019) also note that a significant difference in CLGS would not be required to consider both taxa as conspecific following the unified species concept of de Queiroz (2007) because (i) the status of both taxa as independently evolving lineages (EILs) is automatically maintained by the wide sea barrier and (ii) the existence of these two separate EILs is directly evidenced by their two species’ coalescents in the COI gene.

Here we follow the latter interpretation and consider the Nearctic taxon polaris Curtis, 1835 and Palaearctic taxon pyrrhopygus Friese, 1902 as distinct species, with only Bombus pyrrhopygus occurring in IUCN Europe.Additional work is required to better understand the evolutionary history of this highly interesting species complex.